1. Field of the Invention
This invention relates to a focal-length adjusting unit for photographing apparatuses, provided with an optical system including a variable optical-property element such as a variable focal-length lens or a variable focal-length mirror.
2. Description of Related Art
A lens used for a focusing or variable magnification means of a photographing apparatus or for prevention of the shake thereof has been fabricated by grinding glass. The focal length of the lens cannot be changed by the lens itself, and thus, for example, for focusing, zoom, or a magnification change of a camera, it is necessary to provide a complicated mechanical structure for moving a lens unit along the optical axis.
FIG. 1 shows a camera provided with a conventional focal-length adjusting mechanism. This camera has a lens unit 51 constructed as a photographing lens system in a lens barrel, and includes a movable mirror 10, a pentagonal roof prism 5, an eyepiece 6, a sub-mirror 8, a distance-measuring sensor 9, and an image sensor 7 in a camera body.
The movable mirror 10 is mounted in the camera body to be rotatable around its one side 10a as an axis so that it is inserted in or removed out of the optical path connecting the photographing lens system 51 and the image sensor 7. When the movable mirror 10 is inserted in the optical path, a nearly middle area thereof through which light having passed through the photographing lens system 51 travels, constructed with a half mirror 10b, reflects half of light incident through the photographing lens system 51 to introduce it into the pentagonal roof prism 5 and transmits a remaining half to introduce it into the sub-mirror 8. A one side 8a of the sub-mirror 8 is mounted so that the sub-mirror 8 can be opened and closed with respect to the surface of the movable mirror 10. Specifically, the sub-mirror 8, as shown in FIG. 1, is opened when the movable mirror 10 lies on the optical path, so that it reflects light transmitted through the movable mirror 10 to introduce the light into the distance-measuring sensor 9. When the movable mirror 10 is removed out of the optical path, the sub-mirror 8 is folded and removed out of the optical path.
The pentagonal roof prism 5 is designed to internally reflect three times light reflected by the movable mirror 10 and to introduce an image of an object, as an erect image, into an observer""s pupil through the eyepiece 6.
In such an arrangement, when focusing, zoom, or a magnification change is carried out, at least one part of a lens unit constituting the photographing lens system 51 is moved mechanically along the optical axis so that spacings between lenses of the lens unit are changed to thereby vary the focal length of the whole of photographing lens system 51.
Such a conventional camera, which uses a motor to move the lens unit for focal-length adjustment, increases power consumption and makes a loud noise when the focal-length adjustment is made. Furthermore, there are drawbacks that a response time is long and much time is required to move lenses. There are further drawbacks that even when the camera shake is prevented, as in the above description, lenses are moved mechanically by a motor or a solenoid, and thus power consumption is increased and a mechanical structure is complicated to raise cost.
It is, therefore, an object of the present invention to provide a focal-length adjusting unit for photographing apparatuses which is simple in structure, small in power consumption, and soft in sound, and which is capable of performing zoom, focal-length adjustment, and shake prevention at a short response time, without moving lenses mechanically.
In order to achieve this object, the focal-length adjusting unit for photographing apparatuses of the present invention includes a distance-measuring means for detecting the amount of defocus to an object by using a light beam of the object passing through a photographing optical system; at least two optical elements located in an optical path for distance measurement, deflecting incident light from the object to introduce the light into an image sensor or a distance-measuring sensor; a variable optical-property element constituting at least one of the optical elements, capable of changing the deflection of light in accordance with an applied voltage or an applied current; and a voltage applying means or a current applying means for applying a voltage or a current in accordance with the distance-measuring output of the distance-measuring means. In this case, before a distance measurement is made by the distance-measuring means, the function of light deflection of the variable optical-property element is set to a predetermined value.
Further, the present invention includes a distance-measuring means for detecting the amount of defocus to an object by using a light beam of the object passing through a photographing optical system; at least two mirrors located in an optical path for distance measurement, reflecting incident light from the object to introduce the light into an image sensor or a distance-measuring sensor; a deformable mirror constituting at least one of the mirrors, capable of changing the profile of a reflecting surface in accordance with an applied voltage or an applied current; and a voltage applying means or a current applying means for applying a voltage or a current in accordance with the distance-measuring output of the distance-measuring means. In this case, before a distance measurement is made by the distance-measuring means, the reflecting surface of the deformable mirror is set to a predetermined profile.
Still further, the present invention includes a distance-measuring means for detecting the amount of defocus to an object by using a light beam of the object passing through a photographing optical system; at least two optical elements located in an optical path for distance measurement, refracting incident light from the object to introduce the light into an image sensor or a distance-measuring sensor; a variable focal-length lens constituting at least one of the optical elements, capable of changing the refraction of light in accordance with an applied voltage or an applied current; and a voltage applying means or a current applying means for applying a voltage or a current in accordance with the distance-measuring output of the distance-measuring means. In this case, before a distance measurement is made by the distance-measuring means, the function of refraction of the variable focal-length lens is set to a predetermined value.
This and other objects as well as the features and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments when taken in conjunction with the accompanying drawings.